A typical wireless communication system includes a number of base stations each radiating to provide one or more coverage areas or “cells” in which to serve wireless communication devices (WCDs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices, whether or not user operated. In turn, each base station may sit as a node on a core access network that includes entities such as a network controller, switches and/or gateways, and the core network may provide connectivity with one or more external transport networks such as the public switched telephone network (PSTN) and the Internet. With this arrangement, a WCD within coverage of a base station may engage in air interface communication with the base station and may thereby communicate via the base station with various remote network entities or with other WCDs served by the base station.
Such a system may operate in accordance with a particular air interface protocol, examples of which include, without limitation, Long Term Evolution (LTE) (using orthogonal frequency division multiple access (OFDMA) and single-carrier frequency division multiple access (SC-FDMA)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), and BLUETOOTH. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handover between sectors, and other functions.
In practice, each cell in such a system may operate on one or more carrier frequencies and be modulated or otherwise structured in accordance with the air interface protocol to define resources for carrying communications between the base station and WCDs, including downlink communications in the direction from the base station to WCDs and uplink communications in the direction from WCDs to the base station.
Under CDMA, for instance, the air interface of a cell (or sector) is structure to define a group of spread-spectrum coded channels, some of which are reserved as control channels for carrying control signaling between the base station and WCDs and others of which are assignable by the base station to WCDs on an as-needed basis to carry data traffic. And under LTE, the air interface of a cell is divided over time into a continuum of subframes, each subframe is divided over time and frequency into array of resource elements (mostly 15 kHz by 66.7 microseconds) for carrying modulated data, and certain groups of those resource elements are reserved to define control channels for carrying control signaling between the base station and WCDs, while other groups of the resource elements are assignable by the base station to WCDs on an as-needed basis to carry data traffic.
In a representative wireless communication system, one of the control signals provided on the downlink in each cell is a positioning reference signal (PRS), which is useable to facilitate mobile device positioning. In practice, for instance, in each cell, a PRS could be broadcast in each cell on particular air interface resources, and the location of a WCD could be determined based on the WCD's evaluation of the PRS in each of several cells. For example, using an observed time difference of arrival (OTDOA) process, the WCD could measure a time of arrival (TOA) of the PRS respectively from each of multiple base stations and, using one of the TOAs as a reference, differences between the TOAs could be computed and then used along with known locations of the base stations as a basis to estimate the WCD's location.